1. Field of the Invention
The present invention relates to a control device for threading tubes in crochet galloon looms of the type comprising a thread guide rail provided with an oscillatory motion, a number of threading tubes oscillatory supported by the thread guide rail and individually translatable with respect to said rail against the action exerted by respective first return springs, a number of actuation cables each of them having one end connected to one of said threading tubes, a number of sheaths each slidably engaging one of said actuation cables and having one end fixedly fastened with respect to the thread guide rail and the second end engaged with a fixed support, a number of control plates each engaging at least one of said actuation cables at a second end thereof and being provided with a to-and-fro translation movement with respect to said fixed support in order to cause, through said actuation cables, the translations of said threading tubes against the action of said first return springs, and control means to selectively translate the control plates in synchronism with the movements of said thread guide rail.
2. Prior Art
It is known that there are knitting machines consisting of the association of a crochet galloon loom with a jacquard device. The jacquard device has the function of controlling the movements of the weft yarns in order to enable the formation of very elaborate figured fabrics.
In greater detail, the weft yarns are individually engaged by respective threading tubes oscillatably supported by a thread guide rail provided with combined horizontal and vertical oscillatory motions in synchronism with the movements of the needles. The jacquard device comprises actuation means which, through actuation cables slidably guided within respective sheaths, substantially acts so as to selectively control the positioning, at each working cycle, of the individual threading tubes with respect to the corresponding needles in order to cause the weft yarns to be suitably engaged or not by the needles.
The displacements of each threading tube take place against the action of a first return spring having the function of bringing the tube back to its starting position once the pulling action on the actuation cable has ceased. Also interposed between each actuation cable and the respective threading tube is a second return spring which is stiffer than the first spring and is designed to undergo elastic deformation when the actuation cable, fixedly secured to the selective tensioning means, is still translated within the sheath, after the threading tube has reached its stop position at the end of the stroke. The additional translation of the cable, usually referred to as "extra stroke" represents a useful expedient because it is thus no longer necessary to carry out hard setting ups of the tensioning means and cables for the purpose of being sure that each threading tube is brought to its stop position when its translation is commanded.
In the known art problems have been encountered due to the quick wear of sheaths above all when said sheaths and the corresponding actuation cables have a curved longitudinal extension. This situation for example occurs in knitting machines recently studied and produced by the same applicant, in which the jacquard device is disposed alongside the loom instead of being in superposed relationship with the loom, which happens in traditional knitting machines.
The quick wear of sheaths is due to the sliding friction of the cables in the sheaths, which friction becomes very important as a result of many factors which can be summarized as follows:
high pulling forces applied to the actuation cables to overcome the counter-action of the return springs; PA1 rather important translations of the actuation cables; PA1 curved extension of sheaths and actuation cables.
In greater detail it has been found that the wear of sheaths is above all due to the fact that when the extra stroke is carried out, the actuation cables are translated within the sheaths under the action of rather important forces which are, on the other hand, necessary to overcome the high resistance offered by the second return springs.